1. Field of the Invention
The invention relates to a foldable frame member for a foldable bicycle, more particularly to a foldable bicycle frame member with an improved locking unit.
2. Description of the Related Art
A conventional foldable bicycle (A), such as that shown in FIG. 1, comprises several foldable frame members (A1, A2, A3) which permit folding of the bicycle (A) in order to facilitate storage and transport of the latter when not in use.
An example of a conventional foldable frame member (A1) for the foldable bicycle (A) is shown in FIG. 2. The frame member (A1) is shown to comprise first and second shafts 11, 12, a hinge connector 10 for connecting pivotally the first and second shafts 11, 12 at one end, and a locking unit (B) for retaining releasably the first and second shafts 11, 12 in a coaxial position. The first shaft 11 is to be connected to a bicycle handlebar, while the second shaft 12 is to be connected to a front bicycle fork. The hinge connector 10 includes a first leaf member 100 connected securely to one end of the first shaft 11, a second leaf member 101 connected securely to one end of the second shaft 12, and a hinge pin 102 which connects pivotally first ends of the first and second leaf members 100, 101. The first and second leaf members 100, 101 are preferably welded to the respective one of the first and second shafts 11, 12 and further have second ends provided respectively with a pair of pivot ears 1001, 1011.
Referring to FIGS. 2 and 3, the locking unit (B) comprises a first locking arm 13, an adjustable second locking arm 14, a retaining pin 15, and first and second pivot pins 16, 17. The first locking arm 13 is formed as an elongated member that is generally U-shaped in cross section and that has first and second ends 131, 132 formed respectively with a pair of transverse pivot holes 1310, 1320. The first pivot pin 16 extends through the pivot holes 1310 and the pivot ears 1011 at the second end of the second leaf member 101 to connect pivotally the first end 131 of the first locking arm 13 to the second shaft 12. The second locking arm 14 is formed as a solid rod with a threaded first end 141 and a second end 142 opposite to the first end 141. The retaining pin 15 has a shank portion 151 which extends through the pivot holes 1320 and which is formed with a radial threaded bore 152 that engages the threaded first end 141 of the second locking arm 14, thereby mounting pivotally the first end 141 of the second locking arm 14 to the second end 132 of the first locking arm 13. The second locking arm 14 is shorter and narrower than the first locking arm 13. Thus, the second locking arm 14 can be received in the first locking arm 13 when the first locking arm 13 is pivoted toward the first shaft 11 to retain releasably the first and second shafts 11, 12 in the coaxial position. The second pivot pin 17 is formed with a radial hole 171 that permits extension of the second end 142 of the second locking arm 14 therethrough. A C-shaped locking ring 172 engages the second end 142 of the second locking arm 14 to prevent removal thereof from the second pivot pin 17. The second pivot pin 17 extends through the pivot ears 1001 at the second end of the first leaf member 100 to connect pivotally the second end 142 of the second locking arm 14 to the first shaft 11.
FIG. 2 illustrates the foldable frame member (A1) when in a folded position. To unfold the frame member (A1), the first and second shafts 11, 12 are pivoted to the coaxial position, as shown in FIG. 4. The first locking arm 13 is then pivoted toward the first shaft 11. At this time, the retaining pin 15 is now closer to the first shaft 11 than the second pivot pin 17, and the distance between the retaining pin 15 and the first pivot pin 16 becomes smaller, thereby forcing the first shaft 11 toward the second shaft 12 to achieve a tight locking effect. The force for retaining releasably the first and second shafts 11, 12 in the coaxial position can be adjusted by rotating the second locking arm 14 with the use of a wrench in order to adjust the distance between the retaining pin 15 and the second pivot pin 17, a tighter locking effect being achieved when this distance is reduced.
It is noted that the second locking arm 14 not only serves as a force bearing member but also as an adjustment member. Since the structural strength of the second locking arm 14, which is formed as an elongated solid rod, is weaker than that of the first locking arm 13, which is formed as an elongated member that is generally U-shaped in cross section, and since the two ends 141, 142 of the second locking arm 14 are thinner in order to engage the retaining pin 15 and the second pivot pin 17, the second locking arm 14 is likely to break when a bicycle which employs the foldable frame member (A1) is in use, thereby endangering the user.